The Wilhelm scream is a stock sound effect first recorded in 1951 for the movie Distant Drums. It has been featured in dozens of movies since. Alongside a certain recording of the cry of the red-tailed hawk, it is probably the most well-known cinematic sound cliché.
The Wilhelm's revival came from Star Wars-series Sound Designer Ben Burtt, who tracked down the original recording (which he found as a studio reel labeled "Man being eaten by alligator"), and named it for a character that emitted it in the 1953 movie Charge at Feather River. Its use in Star Wars was the beginning of something of an in-joke amongst some sound designers of the film industry, (especially at Skywalker Sound). They continue to try to incorporate it into movies wherever feasible; action movies are naturals, but film sound cognoscenti are particularly impressed when it is used naturally in films such as A Star Is Born (with Judy Garland) and A Goofy Movie.